Glucagon-like peptide 2 (GLP-2) is a 33 amino-acid gastrointestinal (GI) hormone that is produced by enteroendocrine cells in the small and large intestine and released into circulation after meals. GLP-2 is also expressed in cerebral cortex and astrocytes. GLP-2 exerts its biological responses through specific GLP-2 receptors. GLP-2 is derived from proglucagon processed by prohormone convertase (PC) 1/3. This processing also results in GLP-1, glycentin and oxyntomodulin. When processed in the alpha cells of the pancreas by PC 2, processing of proglucagon results in glucagon.
Overall, GLP-2 coordinates a broad variety of important GI responses including mucosal trophic effect and an increase in intestinal absorption and nutrient assimilation (Lovshin, J. and D. J. Drucker, Ped. Diabetes, 1(1):49-57, 2001); anti-inflammatory activities; mucosal healing and repair; decreasing intestinal permeability to bacteria; and an increase in mesenteric blood flow (Bremholm, L. et al. Scan. J. Gastro. 44(3):314-319, 2009). Such properties are expected to provide therapeutic benefits in a variety of conditions.
GLP-2 plays a role in the intestine from before birth. Various studies of human and animal neonates and infants have examined the role of GLP-2 in intestinal development. GLP-2 is found to be present in human cord blood at birth at levels comparable to adult fasting levels. (Bode, S., et al. Neonatology 91(1) 49-53, 2007.) GLP-2 is secreted in response to feeding and the mechanism by which GLP-2 is secreted is considered to be established at 24 weeks for human neonates. (Yoshikawa, H., et al. Pediatrics Intl. 48(5):464-469, 2006.) GLP-2 and the other proglucagon-derived peptides have role in normal intestinal development and nutrient handling. (Amin, H., et al. Pediatrics 121(1):e180-e186, 2008.) It has also been determined that GLP-2 levels are decreased in preterm infants with feeding intolerance. Therefore, GLP-2 may have therapeutic benefits for such preterm infants. (Ozer, E. A., et al. J. Trop. Pediatr. 55(4): 276-277, 2009.) Necrotizing enterocolitis (NEC) is another condition associated with preterm infants and GLP-2 is associated with protecting against NEC in rats and pigs. (Izumi, H., et al. J. Nutr. 139(7):1322-1327, 2009 and Sangild, P. T., et al. Gastroenterology. 130(6):1776-1792, 2006.) Parenterally fed neonatal pigs suffer from arginine deficiency. Piglets who received additional GLP-2 infusions showed improved levels of arginine synthesis as well as improvements in mucosal mass and villus height in the small intestine. (Urschel, K. L., et al. J. Nutr. 137:601-606, 2007.)
GLP-2 may be of therapeutic benefit to patients with various intestinal conditions including intestinal damage and insufficiency. Specifically, it is suggested that diseases involving malabsorption, inflammation and/or mucosal damage could be ameliorated by treatment with GLP-2. Review articles that give an overview of the therapeutic benefits of GLP-2 include Ziegler, T. R., et al. J Parenter. Enteral Nutr. 23(6 Suppl):5174-5183, 1999; Drucker, D. J., et al. J Parenter. Enteral Nutr. 23(5 Suppl):598-100, 1999; and Estall and Drucker, Ann. Rev. Nutr. 26:391-411, 2006.
Inflammation is a symptom of colitis and the functional changes in the intestine that persist even after resolution of the inflammation have been found to include an increase in GLP-2 immunoreactive L cells. (Lomax, A. E., et al. Am. J. Physiol. Gastrointest. Liver Physiol. 292:G482-G491, 2007.) Treatment of mice with colitis with GLP-2 resulted in a reversal of weight loss, reduction of interleukin-1 expression, and increase of colon length, crypt depth, and mucosal area. This demonstrates that GLP-2 can aid healing of the intestine even in the presence of active inflammation of the intestine. (Drucker, D. J., et al. Am. J. Physiol. Gastrointest. Liver Physiol. 276(1):G79-G91, 1999.) Celiac disease also involves inflammation of the intestine. Studies of humans with celiac disease indicate that GLP-2 may be part of the mucosal healing mechanism for patients with celiac disease. (Caddy, G. R., et al. Eur. J. Gastroenterol. Hepatol. 18(2):195-202, 2006.) Mice with colitis showed reduced inflammation after treatment with GLP-2. Additionally, the mechanism of the anti-inflammatory activity is GLP-2 activation of the suppressor of cytokine signaling (SOCS) 3 pathway. (Ivory, C. P. A., et al. Am. J. Physiol. Gastrointest. Liver Physiol. 295:G1202-G1210, 2008.) As SOCS3 may be involved in tumor suppression (Lund, P. K. and R. J. Rigby, Gastroenterology 131(1):317-319, 2006), GLP-2 activation of the SOCS3 pathway shows that GLP-2 may have protective effects against intestinal cancers.
Barrier function of the epithelial layer of the small intestine is relevant to a number of disorders. Examples include sepsis and bacterial peritonitis. GLP-2 reduces the permeability of the epithelial lining of the small intestine as well as decreasing apoptosis in crypts and villi in the small intestine. (Lovshin and Drucker.) GLP-2's protective effect on the barrier function of the epithelial lining has been shown in burn patients in China. (Wang, S. L. Zhonghua Shoo Shang Za Zhi 24(5):396-9, 2008.) In acute pancreatitis, there is a generalized inflammatory response and the permeability of the intestine increases leading to an increase in transport of bacteria through the epithelium of the intestine. Treatment with GLP-2 in rats with acute pancreatitis decreased intestinal permeability. (Kouris, G. J., et al. Am. J. Surgery 181(6):571-575, 2001.) Additionally, administration of GLP-2 in mice with acute pancreatitis improved immunological function of the intestine. (Kong, L. S., et al. Zhongguo Wei Zhong Bing Ji Jiu Yi Xue. 21(2):103-106, 2009.) Stress-induced reduction in intestinal barrier function in mice has also improved by treatment with GLP-2. (Cameron, H. L. and M. H. Perdue. J Pharmacol Exp Ther. 314(1):214-220, 2005.) Specifically, it has been determined that the treatment with GLP-2 improves barrier function by affecting both the paracellular and transcellular pathways. (Benjamin, M. A., et al. Gut 47:112-119, 2000.) Reduced barrier function has also been implicated in immediate hypersensitivity and late-phase allergic inflammation. (Cameron, H. L., et al. Am. J. Physiol. Gastrointest. Liver Physiol. 284(6):G905-G912, 2003.) Gut barrier function is compromised in diabetic and obese mice leading to metabolic disorders in such mice. Increasing endogenous GLP-2 production in such mice leads to improvement of gut barrier function. (Cani, P. D., et al. Gut 58:1091-1103, 2009.)
Malabsorption in the elderly, which is believed to contribute to malnutrition in that population, has been shown to be reversed by GLP-2. (Drozdowski, L. and A. B. R. Thomson, World J. Gastroenterol. 12(47):7578-7584, 2006.) GLP-2 also regulates absorption of lipids in the intestine as well as the assembly and secretion of triglyceride-right lipoproteins from intestinal enterocytes. (Hsieh, J., et al. Gastroentorology 137(3):997-1005, 2009). Intestinal absorption of lipids was enhanced in humans during GLP-2 administration as evidenced by increased postprandial plasma concentrations of triglycerides and free fatty acids. (Meier, J. J., et al. Gastroenterology 130(1):44-54, 2006.) These results suggest GLP-2 as a treatment for steatorrhea.
Because GLP-2 is secreted in the intestine responsive to intake of food, when a patient's energy intake is other than enterally, the lack of GLP-2 can lead to various side effects in the intestines. Dysfunction in the intestines frequently accompanies cancer and its treatment. In children undergoing cancer treatment it was shown that if energy intake was enterally, the GLP-2 secretion remained normal. (Andreassen, B. U., et al. J. Ped. Gastroenterol. Nutr. 40(1):48-53, 2005.) In pre-term infants whose intestines are not fully developed, feeding is often mostly parenteral with some enteral to promote development of the intestines. Secretion of GLP-2 is important for that development and it has been determined that 40% of total nutrient intake should be enteral in order to ensure normal mucosal proliferation and growth. (Burrin, D. G., et al. Am. J. Clin. Nutr. 71(6):1603-10, 2000.)
Studies of rats on total parenteral nutrition (TPN) shows that TPN results in hypoplasia of the gut mucosa which in turn is associated with a reduction in immune response and an increase in translocation of bacteria from the gut to mesenteric lymph nodes, liver and spleen. Administration of GLP-2 protects against this side effect. (Chance, W. T. et al. Am. J. Gastrointest. Liver Physiol. 273:G559-G563, 1997; Chance, W. T., et al. Peptides, 27(4):883-892, 2006; and Kaji, T., et al. Eur. J. Pharmacol. 596(1-3):138-145.)
GLP-2 has been shown to be involved in the regulation of glucose and may have utility in the treatment of both diabetes and hypoglycemia. De Heer, et al. demonstrated that GLP-2 stimulates glucagon secretion in rat islets. (Diabetologia 50(10):2135-2142, 2007.) Glucagon in turn raises blood glucose levels. Wideman, et al. have shown that by altering the expression of PC in mouse alpha cells from PC2 to PC1/3, proglucagon is processed to yield the products of PC 1/3, (GLP-1, GLP-2, oxyntomodulin) rather than glucagon. The authors suggest therefore utility of GLP-2 in the treatment of diabetes. (Diabetes 56(11):2744-2752, 2007 and Mol. Ther. 17(1):191-198, 2008.)
GLP-2 has utility in the treatment of short bowel syndrome (SBS) and related conditions including intestinal failure. SBS patients treated with GLP-2 for two years showed improvement in various measures including improved renal function, reduction in fecal weight and maintenance of intestinal fluid and electrolyte absorption at lower oral intakes. Jeppesen, P. B., et al. Gastroenterology Research and Practice, 2009, Article 616054. In rats undergoing serial transverse enteroplasty (STEP) for treatment of SBS, postprandial levels of GLP-2 were increased as compared to rats with SBS rats who had not undergone STEP. Additionally, expression of GLP-2 receptor increased. The research suggests that GLP-2 would be useful in guiding use of the STEP procedure. (Kaji, T., et al. J. Ped. Surgery. 44(8):1552-1559, 2009.) Intestinal adaptation after a resection is aided by GLP-2 in rats as well. (Perez, A., et al. J Parenter. Enteral Nutr. 29(2):97-101, 2005; Li, H., et al. Zhonghua Wei Chang Wai Ke Za Zhi 9(1):67-70, 2006; Kaji, T., et al. J. Surg. Res. 152(2):271-280, 2009; and Garrison, A. P., et al. Am. J. Physiol. Gastrointest. Liver Physiol. 296:G643-G650, 2009.)
Intestines can be damaged through both chemotherapy and radiation treatment for cancer. Administration of teduglutide (a GLP-2 analog) prior to gamma irradiation showed a protective effect in mice. (Booth, C., et al. Cell Proliferation 37(6):385-400, 2004.) See also Tones, S., et al. Int J Radiat Oncol Biol Phys. 69(5):1563-1571, 2007. GLP-2 treatment also has a protective effect on the intestine during chemotherapy and aids recovery from damage related to chemotherapy. (Boushey, R. P., et al. Cancer Res. 61:687-693, 2001 and Tavakkolizadeh, A., et al. J. Surg. Res. 91(1):77-82, 2000.)
GLP-2 also mitigates damage to mouse intestines due to nonsteroidal anti-inflammatory drugs (NSAID). (Boushey, R. P., et al. Am. J. Physiol. Endocrinol. Metab. 277(5):E937-E947, 1999.)
GLP-2 is also implicated in gastric relaxation of mice. (Amato, A., et al. Am. J. Physiol. Gastrointest. Liver Physiol. 296:G678-G684, 2009.) Additionally GLP-2 inhibits antral emptying in humans. (Nagell, C. F., et al. Scan. J. Gastroenterol. 39(4):353-358, 2004.) Also related to appetite, GLP-2 inhibits ghrelin secretion in humans. (Banasch, M., et al. Reg. Peptides. 137(3):173-178, 2006.)
GLP-2 has been studied in the brain as well. GLP-2 is involved in astroglial regeneration in rats. (Velázquez, E., et al. Eur. J. Biochem. 270(4):3001-3009, 2003 and Velázquez, E., et al. Mol. Neurobiol. 40:183-193, 2009.) GLP-2 has been shown to have a cytoprotective effect on cells derived from rat central nervous system. (Lovshin, J. A., et al. Endocrinology. 145(7):3495-3506, 2004.) GLP-2 has been shown to have anti-depressant effects in mice. (Iwai, T., et al. Behavioural Brain Res. 204(1):235-240, 2009.) Vrang, N., et al. investigated subgroups of GLP-containing neurons and their functions.) Brain Res. 1149:118-126, 2007.)
GLP-2 has further been shown to be effective in treating osteoporosis. (Henriksen, et al. Bone, 45(5):833-42, 2009.)
Additional research on GLP-2 has investigated GLP-2 and autism (Robertson, M. A., et al. J. Autism Dev. Disord. 38:1066-1071, 2008), GLP-2 and cAMP levels in 3T3-L1 adipocytes (Montrose-Rafizadeh, C. et al. J. Cell. Physiol. 172(3):275-283, 1998)
Native GLP-2 is however not a suitable drug candidate as it is rapidly degraded by peptidases (e.g. DPP IV). It therefore has a very short half-life (t1/2=10 min. in humans) and rapid clearance (CL). Certain GLP-2 analogs with somewhat improved CL relative to hGLP-2 have been created and progressed to clinical development, including [Gly2]hGLP 2 (teduglutide) and ZP-1846 and ZP-1848. (PCT Publication No. WO/2006/117565) Though improved over native GLP-2, it is believed that their pharmacokinetic properties still do not allow for optimal drug dosing, limiting their clinical utility. Therefore, GLP-2 analogs with improved pharmacokinetic properties are needed.